You could go with the Bp in a FC, but like badger said stock for stock you would be goin backwards. Unless you plan a build on it. It would be real nice with a nice potato on it... wouldnt be fast tho..lol i think the Bp prob weighs more than the 13b.. because its iron block.

klze would be an option, the klze bolts up to the miata trannys guts, but the bellhousing is differerent.... but u could get around that..

or you could try the 3.0 v6 jft turbo 3liter outof the jdm mpv..lol